The present invention generally relates to an optical crossconnect apparatus for switching an optical transmission path, and also to an optical transmission system. More specifically, the present invention is directed to an optical crossconnect apparatus capable of recovering a failure of an optical transmission system under economical good connection, and also to an optical network.
Very recently, information infrastructures are prepared and maintained in order to widely progress a so-called “multimedia” typically known as the Internet and CATV in society. To establish highly advanced information social structures, presently available information transmission amounts per one user are considerably increased. To this end, optical fiber networks capable of achieving wide ranges/low loss transmissions are introduced in transport backbones capable of performing long-hand/high-capacity transmissions. In a certain trunk line system constructed of optical fiber network, 10-Gbit data per second may be transmitted in unit of 1 optical fiber. As a result, failures, or troubles occurred in transmission paths, or lines would give serious adverse influences to society, and it is, therefore, very important to maintain the qualities of the network services even when failures happen to occur in transmission paths.
In order that reliability of networks is increased, transmission paths are effectively utilized, and also maintenance operation of transmission path is improved when failures happen to occur, optical crossconnect apparatuses have been positively developed. An optical crossconnect apparatus is installed between optical transmitters/receivers and optical fibers functioning as transmission paths within 1 node of an optical fiber network, and this optical crossconnect apparatus switches optical transmission paths to which optical input/output signals of the optical transmitter/receiver. With employment of such a function, for instance, in the case that a failure happens to occur in a certain working fiber, two sets of optical crossconnect apparatuses provided on both ends of this working fiber switch the connection destination of the optical transmitter/receiver to a protection fiber, so that the failure occurred in the transmission path can be restored.
On the other hand, in an actual optical network, a sufficient amount of protection fibers are not always installed among all of nodes. Accordingly, when a transmission path is recovered from a failure, while using the protection fiber installed between the nodes provided at both ends of the optical fiber where the failure happens to occur, and a third node, an optical signal must be rerouted to another route where no failure occurs so as to recover the failure occurred transmission path. To reroute an optical signal, the transmission length would be extended, and the optical crossconnect apparatus itself of this third node would have loss. To avoid such an insertion loss, an optical signal repeating function is necessarily required for this optical cross-connect apparatus. This repeating function can be realized by that an optical repeater such as an optical amplifier and a regenerator is built in this optical crossconnect apparatus.
As the optical crossconnect apparatus having such an arrangement, for instance, one optical crossconnect apparatus is described in Japanese Electronic Telecommunication Institute Communication Society Conference held in 1996, publication 8-1070, on page 555. Another optical crossconnect apparatus having no optical signal repeating function is described in Japanese Electronic Telecommunication Institute Communication Society Conference held in 1996, publication 8-1083, on page 568.
Furthermore, the optical crossconnect technique is disclosed in Japanese Electronic Telecommunication Communication Institute, Autumn Conference held in 1993 publication SB-8-1, 4-371, on page 372.